"structures composed of hot, electrically charged gas called plasma, which funnel charged particles in towards Saturn. Focusing on the tubes when they initially formed and before they had a chance to dissipate under the influence of the magnetosphere, the scientists found that the occurrence of the tubes correlates with radio wave patterns in the northern and southern hemisphere depending upon the season. This seasonal effect is roughly similar to the way Earth's northern lights appear more frequently in the spring and autumn months.

Radio emissions have been used to measure Jupiter's rotation period reliably, and scientists thought it would also help them determine Saturn's rotation period. To their chagrin, however, the pattern has varied over the visits by different spacecraft and even in radio emissions originating in the northern and southern hemispheres. The new results could help scientists hone in on why these signals vary the way they do."

It doesn't seem like "honing in" is what these guys do for a living...

Saturn has been recognized as a standout since Galileo first pointed his telescope at it. The beauty of the rings immediately draws attention. But Saturn’s invisible radiation belts are special too. Trapped in Saturn’s magnetosphere, the volume of space controlled by the planet’s magnetic field, the radiation belts are only present between zones limited by the orbital distances of the planet’s moons. The radiation disappears where the moons orbit because the particles collide with the moons. The radiation belts themselves should have disappeared long ago because the particles slowly spiral in towards the planet. But the belts are still there!

A recent paper in the Journal of Geophysical Research by Cassini scientists working with an energetic particle detector on the spacecraft’s magnetospheric imaging instrument provides an explanation: Saturn’s radiation belts are regularly replenished through the collision of galactic cosmic rays coming from outside the solar system with atoms in Saturn’s atmosphere and its rings. This phenomenon, known as cosmic ray albedo neutron decay, makes Saturn unique in the solar system and gives scientists a better understanding of the behavior of Saturn’s belts and their differences from Earth’s.

Saturn’s magnetosphere, like those of the other planets, contains radiation belts. These belts consist of ions (atoms that have lost one or more electrons, primarily by collisions or excitation by ultraviolet or x-ray radiation from the sun) and electrons that cycle back and forth along the field lines connecting the north and south magnetic poles. (The ions are mostly the nuclei – single protons – of hydrogen atoms.) After visits by NASA’s Pioneer 11 and Voyager spacecraft, scientists observed that Saturn’s rings and inner satellites absorb these ions and electrons as they orbit around Saturn, clearing zones in the radiation belts. How, then, do the belts maintain themselves over time when the particles slowly drift in, and therefore across the orbits of the satellites?

The graphic shows the donut-shaped structure of Saturn's ion radiation belts, constructed using data from Cassini's energetic charged particle detector known as the the low energy magnetospheric measurement system on Cassini’s magnetospheric imaging instrument. The intensity of the radiation belts is color-coded, with red and blue corresponding to high and low intensities, respectively. Saturn's ion radiation belts extend between the main rings and the orbit of Tethys. The large, inner Saturnian moons (Mimas, Enceladus, Tethys) absorb all high energy ions trapped in magnetic zones that are at the same distances as these satellites’ orbits. (Note how Mimas is particularly effective sweeping particles out of the zone of its orbit, marked by the blue arc in the cross-section.) This results in the formation of “shells” of radiation belts, which are also isolated from the particle populations residing beyond the orbit of Tethys. The intensities are for protons with energies between 12 and 59 million electron volts.Image credit: NASA/JPL-Caltech/MPS/JHUAPL

Roussos and colleagues have found that the rain of local radiation on the moons is maintained by the combination of cosmic rays streaming in from our Milky Way galaxy and the nuclear physics of the cosmic ray collisions at Saturn. Although these kinds of cosmic ray collisions also occur at Earth (and possibly at Jupiter, Uranus and Neptune), the radiation belts of those planets may receive energetic particles through many different mechanisms. At Saturn, cosmic ray collisions appear to be the only process providing high-energy particles, making its radiation belts a unique, filtered reservoir of cosmic ray products from our galaxy.

These cosmic rays are ions themselves and must have enough energy, first, to get inside Saturn’s magnetosphere (which is a barrier to them). The higher the energy of the cosmic rays, the deeper they can penetrate in Saturn’s magnetosphere. Some of these cosmic rays may even make it in as close as the distance of the planet’s main rings or atmosphere. There the collision of a galactic cosmic ray with an atom can shatter the nucleus and release a high energy neutron, one of the constituents of the nucleus of an atom. The important physics in the process is that (1) neutrons are not affected by magnetic fields (so they can travel in any direction) and that (2) neutrons have a limited lifetime: they decay into a lower energy proton, electron, and an anti-neutrino. The proton (and electron) can then become constituents of Saturn’s radiation belts, replenishing particles lost to collisions with Saturn’s moons and rings.

This is a nice picture, but is it correct? Other researchers propose that the now-familiar process of coronal mass ejections from the sun could replenish the radiation belts. Roussos and colleagues point out that three intense solar events collided with Saturn’s magnetosphere and actually generated a temporary new radiation belt outside Tethys’ orbit, a moon orbiting at the outer edge of Saturn’s permanent ion radiation belts. However, no changes were detected in those inner radiation belts throughout this period. Tethys’ absorption of particles apparently isolates the inner radiation belts from events outside. Occasional injections of particles just don’t work to maintain or intensify the inner radiation belts.

Except for some simulations that match the particle energy spectrum observed, there was not observational support for either cosmic ray collisions or an internal acceleration process at work. The Cassini researchers took advantage of Cassini’s long stay studying the Saturn system and the fortuitous coincidence of the extended sunspot minimum just now ending to study any correlation between the behavior of the radiation belts’ intensities over time.

At first glance, cosmic ray collisions and a lack of sunspots would not seem to be related at all. But the galactic cosmic rays that are the engine of cosmic ray albedo neutron decay are modulated by the sun’s behavior. The cosmic rays need to have enough energy to enter the heliosphere (the sun’s version of a planet’s magnetosphere, but with more phenomena). The energy necessary to enter is lower when the sun is less active: this occurs when there are fewer sunspots and fewer solar flares and a weaker magnetic field carried by the solar wind (which is really more like a breeze during sunspot minimum). As a result, the number of galactic cosmic rays reaching Saturn’s magnetosphere is higher during sunspot minimum.

This effect occurs also at our planet and was first established by Scott Forbush in 1937. It is now recognized that there can be long-term Forbush effects tied to the sunspot cycle and short-term Forbush effects due to solar activity like coronal mass ejections. The researchers found evidence of both long- and short-term Forbush effects in their studies of the radiation belts.

In the paper led by Roussos, data from the low energy magnetospheric measurement system on Cassini’s magnetospheric imaging instrument (MIMI/LEMMS) showed that radiation belt intensity rose from the time Cassini arrived at Saturn (June 2004) through the first months of 2010 in step with the rise of the galactic cosmic ray intensity getting into the heliosphere. Then the sun started showing signs of renewed sunspot activity. This finding was in agreement with expectations for radiation belts generated by cosmic rays and represents long term Forbush effects in Saturn’s magnetosphere.

Short-term effects were less obvious but more intriguing. As sunspot activity was falling during the 15-month period spanning the last quarter of 2004 to the start of 2006, three “Solar Energetic Particle” (SEP) events were observed at Saturn. These are enhancements of cosmic rays, but their origin is the sun (solar cosmic rays). Solar energetic particle events can happen anytime but are more frequent when sunspot numbers are high.

Studies at Earth show that these solar cosmic rays supply other planets’ magnetospheres and their radiation belts with a significant number of high energy particles. This is what one would naturally expect to happen.This is not, however, the case for Saturn, in part because Tethys isolates the inner Saturnian belts from particles coming from outside. Solar cosmic ray events “carry” with them a stronger magnetic field, which excludes galactic cosmic rays from their volume. Galactic cosmic ray intensity is therefore reduced when solar cosmic ray events are moving across Saturn’s magnetosphere (these reductions are called “Forbush decreases”). Such Forbush decreases were identified in the MIMI/LEMMS dataset during the “active” 2004 to 2006 period.

Interestingly, during this same period increases in radiation belt intensity were lower (or even absent) compared to the increasing intensities seen between 2006 and 2010. This indicates that Forbush decreases may actually limit the high-energy particle content of Saturn’s radiation belts and even cause a reduction in their intensity (since fewer galactic cosmic rays could enter and have collisions). If this finding is verified by subsequent observations, it may mean that Saturn’s radiation belts are the only ones known to us whose intensity is reduced, instead of being enhanced, after a solar energetic particle event.

Still, some mysteries remain. While cosmic ray collisions may explain the presence of high-energy ions at Saturn, the radiation belts also contain lower energy products. The research team also found that, if the data were separated into lower and higher energy particles in the radiation belts, both behaved the same way. This suggests that both have the same origin or that both might be tied together by some cause-effect relationship, but scientists have not yet understood where the low-energy population comes from or how the high- and low-energy products are related.

Has anyone addressed the questions here yet? Why does earth have charged particles spiraling around it in radiation belts, with no significant rings, while Saturn has particles shaped into rings? Even odder seemingly is that when Saturn does get particles introduced into radiation belts, they quickly end up in the rings? The answer is so simple it is painful. We know that Saturn's dipole magnetic field is aligned almost exactly with it's spin axis, while earth's is tilted at ~11 degrees. All we need is one assumption, that Earth and Saturn are charged, and the rest is straight forward. If a charged particle is sitting anywhere in Saturn's equatorial plane, it will feel a radial attractive (or repulsive) force to the planet. The magnetic field cuts exactly perpendicularly through the equatorial plane (the result of the spin axis aligned dipole). This leaves a force on the particle perpendicular to both the magnetic field and the electric tug, meaning exactly in the plane of the rings, and around the planet. If a charged particle is sitting in Earth's equatorial plane, it will feel a radial attractive (or repulsive) force to the planet. The magnetic field cuts through the plane at angle which varies in a 24 hour cycle, tilting 11 degrees left or right, if you are looking in from the particles perspective, to the planet. This leaves us with a directionally varying force on the particle which sends the particle around the planet, but also up or down through the equatorial plane. The mere act of moving up or down in this case, also drives the particle in or outward, and we have the resulting driven toroidal motion. Going back to Saturn for a minute, we see that even if we introduce a charged particle at a point away from the equatorial plane, it is driven (spiraling) back into the equatorial plane by the magnetic field (this caused by the fact that the magnetic field flows inward toward the planet's poles). So the odd result here, is that even if a charged particle is introduced into earth's equatorial plane, it is driven into toroidal motion by that misaligned dipole field, yet a charged particle outside of Saturn's equatorial plane, is driven into the disk. All this caused simply by a variation in the alignment between a planet's spin axis and it's dipole magnetic field.

Continuing from my last post, we can now see how easy it is to explain Saturn's braided F ring. Saturn's magnetic dipole is aligned very closely to the spin axis, but it's not quite a perfect alignment (estimates from the mainstream of ~1 degree off?). As Saturn rotates, this means that particles in the rings get the ever so slightest nudge out of the ring plane, first in one direction, then the other. Remember, the force on the particle can now be in a direction up to one degree away from the ring plane. If you think this is too small to matter, in general, you'd be right. The rings are sorted, however, (this we both see, and know how it must happen). What we find, is that at some radius (here the F ring), we have a match. The time varying field (caused by Saturn's rotation) is perfect to drive up these particular particles(mass/charge ratio), into toroidal motion. This leaves us with that odd appearing braided ring, right in the middle of an otherwise flat ring system.

An analysis of images of Saturn's moon Enceladus taken from the Cassini Saturn orbiter, reported by Hedman et al.1 on Nature's website today, shows that the output of the giant plume of ice particles, which jets out of fractures in the south polar region of the moon, is controlled by diurnal changes in the tidal stresses from Saturn. The authors find a remarkably strong and simple relationship between the brightness of the plume and Enceladus' position in its orbit around Saturn, providing dramatic confirmation of predictions made in 2007 from a tidal-stress model2.

Those jets just don't look like gravitic structures, imho.

Enceladus' 1.37-day orbit around Saturn is slightly eccentric, as a result of the periodic gravitational influence of the larger moon Dione.

That is really flying !

Tensional stresses would plausibly open pathways for the venting of plume gases and particles, and thus increase plume activity at apoapse.

^ [JPL's theory.]

Cassini has so far made 20 close fly-bys of Enceladus to investigate its surface and interior and to sample its plume. But the plume is large enough and bright enough to be seen by remote sensing from longer range, permitting more frequent study both with Cassini's visible-wavelength cameras and with its Visual and Infrared Mapping Spectrometer (VIMS).

The temporal variations revealed by this analysis are simple and dramatic — the plume is consistently about four times brighter when Enceladus is at apoapse than when it is at periapse,...

Global-ocean models have fallen out of favour for Enceladus, because it is difficult to keep a global ocean from freezing7, and a regional south polar ocean8 is now considered more likely... The VIMS study itself hints at changes in plume ejection speed at different positions in the orbit, offering another handle on how the plume reaches the surface.

Enceladus displays other strikingly clear-cut patterns. For example, its several geological provinces, defined by age and style of surface deformation, are arranged with almost perfect symmetry around its spin axis and the direction of Saturn10. Equally strange is the geometric simplicity of the four active tiger-stripe fractures, all roughly the same length (about 130 km), and evenly spaced about 35 km apart. As with the plume behaviour, such simple patterns must point to important truths, but these other puzzles remain mysterious, and definitive explanations await future research.

The hot spot’s behavior should be variable like that on Venus and correlated with the appearance of Saturn’s ring spokes, which are a visible manifestation of a heightened equatorial discharge in that part of Saturn’s Faraday motor circuit. The Electric Universe also predicts, experimentum crucis, that BOTH poles should be hot, not one hot and the other cold.